**3. Problem Statement**

The cited examples show significant progress in the development of VPPs. However, this article aims to highlight technical aspects at the preliminary stage of the concept and operation planning of a VPP. The size of the ESS, the capacity of available power generation, as well as control restrictions on the use of the DER and ESS have to be identified. The cited examples are also of interest due to permanent amendments of standards and network codes. This is why the problem has its beginnings in the technical requirements of the cooperation of power generation units and energy storage systems with a power system. The aim of this section is firstly to generally review the technical requirements dedicated to controlling the DER and ESS in terms of their cooperation with the power system and then to select and discuss in detail several topics which can appear on the primary level of VPP planning. Among the wide list of technical aspects, this paper presents three of them. They were selected due to the association of the VPP project with the distribution network and small generation units. Thus, the technical aspects presented in this section serve as the base for further investigation of the following problems:

